There will be residual DC voltage on the bus of GIS equipment after the circuit breaker and disconnector are opened. Due to the low leakage velocity in GIS

the residual DC voltage can remain for several hours. When the switch is re-closed

an operating overvoltage will be generated. The overvoltage will be superimposed on the residual DC voltage existing in the bus

putting GIS under combined voltage of DC and impulse. Many domestic accidents of GIS occurred at the moment of switch closing

so it is necessary to study the discharge characteristics of GIS undercombined voltage of DC and impulse. In order to clarify the current research status and to serve as reference in engi-neering and academic research

this paper summarizes the research on the discharge characteristics of GIS under combined voltage of DC and impulse at home and abroad. First

the discharge characteristics and discharge mechanism of SF6 gas gap in quasi-uniform electric field and nonuniform electric field under combined voltage of DC andimpulse are introduced

as well as the discharge characteristics caused by the free metal particles;Then the flashover characteristics of insulators under combined voltage of DC and impulse and the influence of metal particles on the flashover characteristics of insulators are summarized

and the research status of the influence mechanism of surface charge on the flashover process of insulators is analyzed. Finally

the existing problems and future research directions are summarized.